Carbon, hydrogen, oxygen, nitrogen, phosphorus and sulphur are the primary elements essential to all life. Soils contain all of these elements in addition to other macronutrients and micronutrients which are needed for plant growth. Typically, such elements are not present in the soil in sufficient quantity or in forms that can support maximum plant growth and yield. In order to overcome these deficiencies, fertilizers having specific chemical constituents in specific amounts are often added to the soil, thereby enriching the growth medium. The fertilizers may be supplemented with certain trace elements such as copper, iron, manganese, zinc, cobalt, molybdenum, and boron, as oxides or salts containing the elements in the cationic form.
Agriculturally, metal ions are essential nutrients for plant growth. Soil deficiency because of the unavailability or exhaustion of metal ions is very often the cause of poor plant growth.
Acidification of soil may be needed when soil pH is high or when naturally occurring calcium carbonates are present. For example, when pH is above about 7.5, the solubility of phosphorous and the metal micronutrients such as iron, manganese and zinc are limited. Thus, generating a zone of acidification where the solubility of the fertilizers is enhanced promotes plant growth by increasing nutrient availability.